This invention relates generally to food and beverage packagings and, more particularly, to oxygen barrier laminate structures for producing aseptic packagings and containers.
Heat-sealable low density polyethylenes are popular components of current paperboard food and non-food packagings and containers. To provide a suitable barrier to oxygen and light transmission, structures with materials such as aluminum foil have been utilized in the production of these paperboard packagings. However, the unrestricted use of aluminum foil in any packaging renders that packaging non-microwaveable.
Oxygen permeability is a key consideration in aseptic, shelf-stable packaging because if oxygen is allowed to react with a food or beverage product it can result in deterioration of many aspects of product quality. Attempts have been made to produce an oxygen barrier container without the use of aluminum foil. One such type of container also has the requirement that the laminate used to form the container must have a very thin inner or product contact layer (0.7 mil or less) of low density polyethylene (LDPE) in order to achieve its desired results of minimizing absorption of essential flavor oils contained in citrus juice and other beverage products. Such a thin product contact layer is not acceptable in the aseptic packaging of the present invention because it cannot provide for commercial sterilization.
The present invention involves aseptic packaging which means commercially sterile packaging having no living microorganisms capable of growth inside the sealed container.
Aseptic packaging can provide shelf life of up to a year or more prior to opening without the need for preservatives or refrigeration. Conversely traditional gable top cartons (commonly used for the non-aseptic packaging of milk and juice) rely on refrigeration to retard microbial activity. But even under refrigeration, the shelf life of milk or juice in a non-aseptic carton is limited, in part due to the lack of adequate package seals for keeping the product isolated from outside microorganisms.
The produce contact surface of aseptic packaging is sterilized separately from the product itself. Thus, when the package is filled with pre-sterilized product, the inner seals of the packaging must be free of microorganisms. All such inner seals (formed when the laminated structure is folded and bonded to itself to form a desired container shape) should have no unfilled voids or cavities where microorganisms may be shielded from the sterilizing process.
To fill such voids in aseptic packaging of the present invention, the inner, product contact layer is preferably thick to an extent that it will adequately "flow" during formation of the aseptic package seals and thereby fill any such voids or cavities inside the package.
In one method of manufacturing the aseptic packaging of the present invention, a flat card ("blank") is first produced which is made of several layers of material bonded together. This multi-layer structure composition is the subject of the present patent application. In one type of packaging of the present invention, the blank takes the final form of a rectangular shaped box enclosed on all six sides (top, bottom, and four walls) of the box.
In the manufacturing process of the packaging material, the final step is to form a sleeve, for example as described in U.S. Pat. No. 4,239,150. In this step, the two sides of the flat multi-layer blank are brought together to form a back seam by flame sealing, thus producing the sleeve.
In the aseptic filling process, the sleeve is placed on a mandrel which allows for the formation of the bottom seals of the package. The bottom seals are formed by heat and pressure, utilizing the thick LDPE inner layer of the multi-layer sleeve. The heat applied to the inner-most layer of the multi-layer sleeve enables it to "flow" to fill voids and cavities. The interior of the open-top box, including all inner seal areas, is then sterilized with hydrogen peroxide vapor which is then evaporated. Sterilized product is then deposited through the top opening to fill the box. The top portion of the box is then closed and thermally sealed.
Thus the seals formed in an aseptic package serve a structural (i.e., rigidity), a mechanical (i.e., liquid tight) and a biological (i.e., microbial seal) purpose.
In addition to oxygen impermeability, aluminum foil also serves a light barrier function. Packaging not containing aluminum foil may require other means to block or inhibit light transmission in order to preserve product quality. Light penetration of packaging material results in chemical reactions in some products which adversely affect the qualities of taste, smell, color, shelf life, etc.
As many units of measurement are discussed in the description of the present invention, the following conversions are appropriate for purposes of this discussion:
______________________________________ CONVERSON FACTORS* ______________________________________ LDPE** (density .917) 1 mil = 23.30 g/m.sup.2 10 g/m.sup.2 = .429 mil EVOH** (density 1.18) 1 mil = 29.98 g/m.sup.2 10 g/m.sup.2 = .334 mil ______________________________________ *1 mil = 1/1000 inch 1 m.sup.2 = 1 square meter 1 g = 1/1000 kilogram 1 ream = 3000 sq. ft. **EVOH Ethylene Vinyl Alcohol **LDPE Low Density Polyethylene